Silicone rubber, fouling-resistant compositions are described for example in UK Patents 1307001, 1470465 and 1581727, UK Patent Application 2141436, European Patent 16195 and U.S. Pat. No. 3,702,778. They have significant advantages over conventional anti-fouling compositions containing marine biocides which are gradually leached from the paint. The silicone rubber coatings rely on their low surface energy, rather than on biocides, to inhibit settlement of marine organisms. There has been some concern about the release of triorganotin biocides, one of the most effective and widely used types of marine biocide, from paint on the hulls of yachts and pleasure boats. Moreover, conventional anti-fouling paints eventually become ineffective as all their biocide is released. Silicone rubber coatings are potentially capable of retaining their low energy surface indefinitely.
There are, however, practical difficulties in the use of silicone rubber, fouling-resistant compositions, especially as coatings for ships' hulls. They are mechanically rather weak; in particular they have low tear strength and low cohesive strength so that the paint film is easily damaged.
European Patent 32597 describes an anti-fouling coating comprising a vulcanised silicone rubber, which rubber contains grafted silicon-free segments which are constituted of recurrent units of ethylenically unsaturated monomers such as butyl acrylate or styrene. This coating is described as having a high cohesive strength, but in practice has been found to give reduced anti-fouling properties.
European Patent Application 89071 describes a similar silicone rubber containing grafted silicon-free segments which are preferably derived from polymerisation of ethylenically unsaturated monomers. It mentions that the silicon-free segments can be derived from urethane-based units. Polyurethane segments can be attached to silicon atoms of the silicone rubber by means of an oxyphenylene group or an amino-phenylene group.
British Patent 1477055 describes an anti-icing coating of a polyurethane prepared from an isocyanate functional material and a polycarbinol silicone.